RF Module UpdatesFor users of the RF Module, COMSOL Multiphysics® version 5.2a brings new simulation methods for faster bandpass-filter type device design, new capability for modeling radar cross sections, and more. Review all of the RF Module updates in further detail below.
Fast Modeling Approach for Bandpass-Filter Type Devices
Two powerful simulation methods have been implemented in existing Application Library examples for designing bandpass-filter type high-Q devices: the asymptotic waveform evaluation and frequency-domain modal methods. These perform simulations at speeds that are orders of magnitude faster than conventional frequency sweeping for these devices.
When simulating bandpass-filter type high-Q devices using the finite element method (FEM) in the frequency domain, you often encounter situations that require detailed frequency sweeps to describe the passband adequately and accurately. Simulation time is directly proportional to the number of frequencies included during the simulation sweep. These new methods substantially reduce the computational time.
Application Library path for the example using the asymptotic Waveform Evaluation method:
Application Library path for the examples using the Frequency-Domain Modal method:
Postprocessing Far-Field Variables for Bistatic Radar Cross Section (RCS)
Postprocessing variables have been added to the physics interfaces that calculate bistatic radar cross sections (RCS). These postprocessing variables can be used in far-field plots to visualize the size of a scatterer as seen by a radar. The bistatic RCS variable, bRCS3D, describes the RCS measured through a transmitter and receiver that are located separately, and you can also plot monostatic RCS. For 2D models, you can model the bistatic RCS per unit length using the operator bRCS2D.
Application Library path for an example plotting bistatic RCS using the bRCS3D postprocessing variable:
Application Library path for an example plotting monostatic RCS using the bRCS2D postprocessing variable:
Two-Port Network Systems
The Two-Port Network feature characterizes the response of a two-port network system, such as reflection and transmission, using S-parameters. Just like the Lumped Port feature, the Two-port Network feature can only be applied on boundaries that extend between two metallic boundaries where the Perfect Electric Conductor, Impedance Boundary, or Transition Boundary conditions apply, which are separated by a distance much smaller than the wavelength. A pair of Two-Port Network Port subnodes are added by default to the Two-Port Network node and are used to select boundaries corresponding to Port 1 and Port 2 in the S-parameter input, respectively.
Updates to Perfectly Matched Layers (PMLs)
Several options have been added to the Perfectly Matched Layer feature that make it possible to customize the layer properties:
- The option Enable/disable PMLs in the solver is useful for modeling scattering problems where the source is a computed field.
- The user-defined geometry type option is available if the PML has a nonstandard geometry, and can also be used if the automatic PML geometry detection fails.
- You can choose user-defined coordinate stretching functions for defining the PML scaling. This allows you to tailor the scaling inside a PML, for example, to very efficiently absorb waves in specific physics configurations.
Updated App: Plasmonic Wire Grating Analyzer
Surface plasmon-based circuits are being used in applications such as plasmonic chips, light generation, and nanolithography. The Plasmonic Wire Grating Analyzer application computes the coefficients of refraction, specular reflection, and first-order diffraction as functions of the angle of incidence for a plasmonic wire grating on a dielectric substrate.
The model describes a unit cell of the grating, where Floquet boundary conditions define the periodicity. Postprocessing functionality allows you to expand the number of unit cells and extract the visualization into the third dimension.
Built into the app is the ability to sweep the incident angle of a plane wave from the normal angle to the grazing angle on the grating structure. The app also allows you to vary the radius of a wire as well as the periodicity or size of the unit cell. Further parameters that can be varied are the wavelength and orientation of the polarization.
The application presents results for the electric field norm for multiple grating periodicity for selected angles of incidence, the incident wave vector and wave vectors for all reflected and transmitted modes, and the reflectance and transmittance.
Application Library path: RF_Module/Applications/plasmonic_wire_grating
The Plasmonic Wire Grating Analyzer app computes diffraction efficiencies for the transmitted and reflected waves and the first and second diffraction orders for a wire grating on a dielectric substrate. The wavelength, polarization, material properties, wave periodicity, and radius can be changed.
New Tutorial Model: Log-Periodic Antenna for EMI/EMC Testing
The shape of a log-periodic antenna resembles that of a Yagi-Uda antenna, but is composed of a coplanar array to achieve a wider bandwidth. It is also known as a wideband or frequency-independent antenna.
All metallic parts are modeled using the perfect electric conductor (PEC) boundary conditions. The antenna is excited by a lumped port while a lumped element with a resistor is used to terminate the excitation.
Results show the impedance matching properties on a Smith plot as well as a far-field polar plot, which shows that the directionality of the radiation pattern varies slightly as frequency increases. A 3D far-field radiation pattern shows the same tendency. Also presented is the voltage-standing-wave-ratio (VSWR) of the antenna.
Application Library path: RF_Module/Antennas/log_periodic_antenna
A log-periodic antenna is modeled by fitting a coplanar dipole array through two metallic body frames. The far-field radiation pattern and the norm of electric field on a coplanar dipole array are visualized.
New Tutorial Model: Signal Integrity (SI) and Time-Domain Reflectometry (TDR) Analysis of Adjacent Microstrip Lines
A signal integrity (SI) analysis gives an overview of the quality of an electrical signal transmitted through electrical circuits, such as high-speed interconnects, cables, and printed circuit boards. The quality of the received signal can be distorted by noise from outside the circuit, and can be degraded by impedance mismatch, insertion loss, and crosstalk. For this reason, EMC/EMI analyses are run to estimate the susceptibility of a device or a network to an undesired coupling.
In this tutorial model, we examine the crosstalk effect between two adjacent microstrip lines on a microwave substrate with a constant dielectric constant. Two pulses are applied to the device where a parametric sweep switches the frequency of the pulse during the simulation.
The simulation presents the time-domain reflectometry (TDR) response at the coupled ports, which shows increased distortion of the signals at higher frequency or data rates.
Application Library path: RF_Module/Transmission_Lines_and_Waveguides/microstrip_line_crosstalk
A microstrip line crosstalk model is composed of a microwave substrate, with a ground plane and two adjacent microstrip lines. The contour plot of the logarithmic norm of electric field shows the coupling of the electric field between the two microstrip lines.